Yes true - in general the wood on the older models was better.
However the playing quality of a clarinet depends on many other things as well, so in the end you have to play it to find out.
But in principle if (big if) you can find an older "A" R13 in good condition, then the chances are that it could be better than a new one.

2 other pluses
Older wood is more stable and less likely to crack
"A" clarinets tend to lead a more gentle life and so likely to suffer less wear.